[PATCH] video: hyperv_fb: Directly use the MMIO VRAM

From: Dexuan Cui
Date: Fri Nov 20 2020 - 20:47:10 EST

Late in 2019, 2 commits (see the 2 Fixes tags) were introduced to
mitigate the slow framebuffer issue. Now that we have fixed the
slowness issue by correctly mapping the MMIO VRAM (see
commit 5f1251a48c17 ("video: hyperv_fb: Fix the cache type when mapping
the VRAM")), we can remove most of the code introduced by the 2 commits,
i.e. we no longer need to allocate physical memory and use it to back up
the VRAM in Generation-1 VM, and we also no longer need to allocate
physical memory to back up the framebuffer in a Generation-2 VM and copy
the framebuffer to the real VRAM.

synthvid_deferred_io() is kept, because it's still desirable to send the
SYNTHVID_DIRT message only for the exact dirty rectangle, and only when
needed.

Fixes: d21987d709e8 ("video: hyperv: hyperv_fb: Support deferred IO for Hyper-V frame buffer driver")
Fixes: 3a6fb6c4255c ("video: hyperv: hyperv_fb: Use physical memory for fb on HyperV Gen 1 VMs.")
Cc: Wei Hu <weh@xxxxxxxxxxxxx>
Cc: Boqun Feng <boqun.feng@xxxxxxxxx>
Signed-off-by: Dexuan Cui <decui@xxxxxxxxxxxxx>
---

This patch changes drivers/video/fbdev/Kconfig, but I hope this can
still go through the Hyper-V tree
https://git.kernel.org/pub/scm/linux/kernel/git/hyperv/linux.git/log/?h=hyperv-next
because it's unlikely to cause any build issue to other fbdev drivers
(that line was introduced by 3a6fb6c4255c only for hyperv_fb.c)

Note: this patch is based on the Hyper-V tree's hyperv-fixes branch, but
it should also apply cleanly to the branch hyperv-next if the commit
5f1251a48c17 is applied first. This patch is for v5.11 rather than
v5.10.

drivers/video/fbdev/Kconfig | 1 -
drivers/video/fbdev/hyperv_fb.c | 170 ++------------------------------
2 files changed, 9 insertions(+), 162 deletions(-)

diff --git a/drivers/video/fbdev/Kconfig b/drivers/video/fbdev/Kconfig
index 402e85450bb5..05b37fb3c6d6 100644
--- a/drivers/video/fbdev/Kconfig
+++ b/drivers/video/fbdev/Kconfig
@@ -2205,7 +2205,6 @@ config FB_HYPERV
select FB_CFB_COPYAREA
select FB_CFB_IMAGEBLIT
select FB_DEFERRED_IO
- select DMA_CMA if HAVE_DMA_CONTIGUOUS && CMA
help
This framebuffer driver supports Microsoft Hyper-V Synthetic Video.

diff --git a/drivers/video/fbdev/hyperv_fb.c b/drivers/video/fbdev/hyperv_fb.c
index 58c74d2356ba..8131f4e66f98 100644
--- a/drivers/video/fbdev/hyperv_fb.c
+++ b/drivers/video/fbdev/hyperv_fb.c
@@ -31,16 +31,6 @@
* "set-vmvideo" command. For example
* set-vmvideo -vmname name -horizontalresolution:1920 \
* -verticalresolution:1200 -resolutiontype single
- *
- * Gen 1 VMs also support direct using VM's physical memory for framebuffer.
- * It could improve the efficiency and performance for framebuffer and VM.
- * This requires to allocate contiguous physical memory from Linux kernel's
- * CMA memory allocator. To enable this, supply a kernel parameter to give
- * enough memory space to CMA allocator for framebuffer. For example:
- * cma=130m
- * This gives 130MB memory to CMA allocator that can be allocated to
- * framebuffer. For reference, 8K resolution (7680x4320) takes about
- * 127MB memory.
*/

#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
@@ -267,16 +257,8 @@ struct hvfb_par {
/* If true, the VSC notifies the VSP on every framebuffer change */
bool synchronous_fb;

- /* If true, need to copy from deferred IO mem to framebuffer mem */
- bool need_docopy;
-
struct notifier_block hvfb_panic_nb;

- /* Memory for deferred IO and frame buffer itself */
- unsigned char *dio_vp;
- unsigned char *mmio_vp;
- phys_addr_t mmio_pp;
-
/* Dirty rectangle, protected by delayed_refresh_lock */
int x1, y1, x2, y2;
bool delayed_refresh;
@@ -405,21 +387,6 @@ synthvid_update(struct fb_info *info, int x1, int y1, int x2, int y2)
return 0;
}

-static void hvfb_docopy(struct hvfb_par *par,
- unsigned long offset,
- unsigned long size)
-{
- if (!par || !par->mmio_vp || !par->dio_vp || !par->fb_ready ||
- size == 0 || offset >= dio_fb_size)
- return;
-
- if (offset + size > dio_fb_size)
- size = dio_fb_size - offset;
-
- memcpy(par->mmio_vp + offset, par->dio_vp + offset, size);
-}
-
-/* Deferred IO callback */
static void synthvid_deferred_io(struct fb_info *p,
struct list_head *pagelist)
{
@@ -444,10 +411,6 @@ static void synthvid_deferred_io(struct fb_info *p,
y2 = end / p->fix.line_length;
miny = min_t(int, miny, y1);
maxy = max_t(int, maxy, y2);
-
- /* Copy from dio space to mmio address */
- if (par->fb_ready && par->need_docopy)
- hvfb_docopy(par, start, PAGE_SIZE);
}

if (par->fb_ready && par->update)
@@ -704,7 +667,7 @@ static int synthvid_send_config(struct hv_device *hdev)
msg->vid_hdr.type = SYNTHVID_VRAM_LOCATION;
msg->vid_hdr.size = sizeof(struct synthvid_msg_hdr) +
sizeof(struct synthvid_vram_location);
- msg->vram.user_ctx = msg->vram.vram_gpa = par->mmio_pp;
+ msg->vram.user_ctx = msg->vram.vram_gpa = info->fix.smem_start;
msg->vram.is_vram_gpa_specified = 1;
synthvid_send(hdev, msg);

@@ -714,7 +677,7 @@ static int synthvid_send_config(struct hv_device *hdev)
ret = -ETIMEDOUT;
goto out;
}
- if (msg->vram_ack.user_ctx != par->mmio_pp) {
+ if (msg->vram_ack.user_ctx != info->fix.smem_start) {
pr_err("Unable to set VRAM location\n");
ret = -ENODEV;
goto out;
@@ -740,7 +703,6 @@ static void hvfb_update_work(struct work_struct *w)
struct fb_info *info = par->info;
unsigned long flags;
int x1, x2, y1, y2;
- int j;

spin_lock_irqsave(&par->delayed_refresh_lock, flags);
/* Reset the request flag */
@@ -762,14 +724,6 @@ static void hvfb_update_work(struct work_struct *w)
y1 > info->var.yres || y2 > info->var.yres || x2 <= x1)
return;

- /* Copy the dirty rectangle to frame buffer memory */
- if (par->need_docopy)
- for (j = y1; j < y2; j++)
- hvfb_docopy(par,
- j * info->fix.line_length +
- (x1 * screen_depth / 8),
- (x2 - x1) * screen_depth / 8);
-
/* Refresh */
if (par->fb_ready && par->update)
synthvid_update(info, x1, y1, x2, y2);
@@ -813,8 +767,6 @@ static int hvfb_on_panic(struct notifier_block *nb,
par = container_of(nb, struct hvfb_par, hvfb_panic_nb);
par->synchronous_fb = true;
info = par->info;
- if (par->need_docopy)
- hvfb_docopy(par, 0, dio_fb_size);
synthvid_update(info, 0, 0, INT_MAX, INT_MAX);

return NOTIFY_DONE;
@@ -953,62 +905,6 @@ static void hvfb_get_option(struct fb_info *info)
return;
}

-/*
- * Allocate enough contiguous physical memory.
- * Return physical address if succeeded or -1 if failed.
- */
-static phys_addr_t hvfb_get_phymem(struct hv_device *hdev,
- unsigned int request_size)
-{
- struct page *page = NULL;
- dma_addr_t dma_handle;
- void *vmem;
- phys_addr_t paddr = 0;
- unsigned int order = get_order(request_size);
-
- if (request_size == 0)
- return -1;
-
- if (order < MAX_ORDER) {
- /* Call alloc_pages if the size is less than 2^MAX_ORDER */
- page = alloc_pages(GFP_KERNEL | __GFP_ZERO, order);
- if (!page)
- return -1;
-
- paddr = (page_to_pfn(page) << PAGE_SHIFT);
- } else {
- /* Allocate from CMA */
- hdev->device.coherent_dma_mask = DMA_BIT_MASK(64);
-
- vmem = dma_alloc_coherent(&hdev->device,
- round_up(request_size, PAGE_SIZE),
- &dma_handle,
- GFP_KERNEL | __GFP_NOWARN);
-
- if (!vmem)
- return -1;
-
- paddr = virt_to_phys(vmem);
- }
-
- return paddr;
-}
-
-/* Release contiguous physical memory */
-static void hvfb_release_phymem(struct hv_device *hdev,
- phys_addr_t paddr, unsigned int size)
-{
- unsigned int order = get_order(size);
-
- if (order < MAX_ORDER)
- __free_pages(pfn_to_page(paddr >> PAGE_SHIFT), order);
- else
- dma_free_coherent(&hdev->device,
- round_up(size, PAGE_SIZE),
- phys_to_virt(paddr),
- paddr);
-}
-

/* Get framebuffer memory from Hyper-V video pci space */
static int hvfb_getmem(struct hv_device *hdev, struct fb_info *info)
@@ -1018,7 +914,6 @@ static int hvfb_getmem(struct hv_device *hdev, struct fb_info *info)
void __iomem *fb_virt;
int gen2vm = efi_enabled(EFI_BOOT);
resource_size_t pot_start, pot_end;
- phys_addr_t paddr;
int ret;

info->apertures = alloc_apertures(1);
@@ -1036,38 +931,12 @@ static int hvfb_getmem(struct hv_device *hdev, struct fb_info *info)

info->apertures->ranges[0].base = pci_resource_start(pdev, 0);
info->apertures->ranges[0].size = pci_resource_len(pdev, 0);
-
- /*
- * For Gen 1 VM, we can directly use the contiguous memory
- * from VM. If we succeed, deferred IO happens directly
- * on this allocated framebuffer memory, avoiding extra
- * memory copy.
- */
- paddr = hvfb_get_phymem(hdev, screen_fb_size);
- if (paddr != (phys_addr_t) -1) {
- par->mmio_pp = paddr;
- par->mmio_vp = par->dio_vp = __va(paddr);
-
- info->fix.smem_start = paddr;
- info->fix.smem_len = screen_fb_size;
- info->screen_base = par->mmio_vp;
- info->screen_size = screen_fb_size;
-
- par->need_docopy = false;
- goto getmem_done;
- }
- pr_info("Unable to allocate enough contiguous physical memory on Gen 1 VM. Using MMIO instead.\n");
} else {
info->apertures->ranges[0].base = screen_info.lfb_base;
info->apertures->ranges[0].size = screen_info.lfb_size;
}

- /*
- * Cannot use the contiguous physical memory.
- * Allocate mmio space for framebuffer.
- */
- dio_fb_size =
- screen_width * screen_height * screen_depth / 8;
+ dio_fb_size = screen_width * screen_height * screen_depth / 8;

if (gen2vm) {
pot_start = 0;
@@ -1101,22 +970,11 @@ static int hvfb_getmem(struct hv_device *hdev, struct fb_info *info)
if (!fb_virt)
goto err2;

- /* Allocate memory for deferred IO */
- par->dio_vp = vzalloc(round_up(dio_fb_size, PAGE_SIZE));
- if (par->dio_vp == NULL)
- goto err3;
-
- /* Physical address of FB device */
- par->mmio_pp = par->mem->start;
- /* Virtual address of FB device */
- par->mmio_vp = (unsigned char *) fb_virt;
-
info->fix.smem_start = par->mem->start;
info->fix.smem_len = dio_fb_size;
- info->screen_base = par->dio_vp;
+ info->screen_base = fb_virt;
info->screen_size = dio_fb_size;

-getmem_done:
remove_conflicting_framebuffers(info->apertures,
KBUILD_MODNAME, false);
if (!gen2vm)
@@ -1125,8 +983,6 @@ static int hvfb_getmem(struct hv_device *hdev, struct fb_info *info)

return 0;

-err3:
- iounmap(fb_virt);
err2:
vmbus_free_mmio(par->mem->start, screen_fb_size);
par->mem = NULL;
@@ -1139,19 +995,12 @@ static int hvfb_getmem(struct hv_device *hdev, struct fb_info *info)
}

/* Release the framebuffer */
-static void hvfb_putmem(struct hv_device *hdev, struct fb_info *info)
+static void hvfb_putmem(struct fb_info *info)
{
struct hvfb_par *par = info->par;

- if (par->need_docopy) {
- vfree(par->dio_vp);
- iounmap(info->screen_base);
- vmbus_free_mmio(par->mem->start, screen_fb_size);
- } else {
- hvfb_release_phymem(hdev, info->fix.smem_start,
- screen_fb_size);
- }
-
+ iounmap(info->screen_base);
+ vmbus_free_mmio(par->mem->start, screen_fb_size);
par->mem = NULL;
}

@@ -1170,7 +1019,6 @@ static int hvfb_probe(struct hv_device *hdev,
par = info->par;
par->info = info;
par->fb_ready = false;
- par->need_docopy = true;
init_completion(&par->wait);
INIT_DELAYED_WORK(&par->dwork, hvfb_update_work);

@@ -1256,7 +1104,7 @@ static int hvfb_probe(struct hv_device *hdev,

error:
fb_deferred_io_cleanup(info);
- hvfb_putmem(hdev, info);
+ hvfb_putmem(info);
error2:
vmbus_close(hdev->channel);
error1:
@@ -1286,7 +1134,7 @@ static int hvfb_remove(struct hv_device *hdev)
vmbus_close(hdev->channel);
hv_set_drvdata(hdev, NULL);

- hvfb_putmem(hdev, info);
+ hvfb_putmem(info);
framebuffer_release(info);

return 0;
--
2.19.1